1. Field of the Invention:
The present invention relates to amorphous superconducting alloys containing a major amount of a transition metal and, more particularly, to metal glasses containing a small amount of small crystalline flux pinning centers.
2. Description of the Prior Art:
A useful material for superconducting magnet windings must possess the following properties:
(a) The material must be produced in the form of wires or ribbons suitable for winding a magnet;
(b) The mechanical properties of the material must be such that the material can be bent during winding. Brittle materials are not desirable;
(c) The superconducting transition temperature must be well above 4.2.degree. K. to allow for convenient operation in liquid helium;
(d) The upper critical field H.sub.c2 at 4.2.degree. K. must be greater than the field at which the magnet is expected to operate;
(e) The critical current density J.sub.c in the expected operating field must be large-typically of order 10.sup.5 A/cm.sup.2 for fields in the 100 KOe range.
Present commercial superconducting alloys used for superconducting wires for magnet windings are crystalline NbTi and Nb.sub.3 Sn, alloys. The superconducting transition temperature, critical field and critical current density for these alloys are presented in Table 1, below
______________________________________ Alloy Composition Tc(K) H.sub.c2,T = 4.2 Jc (KOe) 1 = 50 KOe NbTi 9-10 120 10.sup.5 A/cm.sup.2 Nb.sub.3 Sn 18 220 10.sup.6 A/cm.sup.2 ______________________________________
NbTi exhibits limited ductility and Nb.sub.3 Sn exhibits essentially no ductility. Both alloys require very difficult ribbon fabrication procedures. NbTi is cast into ingots, cold worked and drawn into ribbons. Nb.sub.3 Sn must be drawn dispersed in a ductile copper matrix since it has no ductility by itself. Both of these alloys are very susceptible to damage in a thermal neutron environment requiring shielding when used as magnets for plasma fusion devices, the transition temperature dropping to about 3 K.
Amorphous superconductors readily prepared by liquid quenching in the forms of wires and ribbons have been shown to be ductile and flexible, have transition temperatures in the range of 9.degree.-10.degree. K. and critical fields ranging up to 200 KOe. However, the critical current density in the expected operation field is too low to be practical.